By richer contents of cellular phones and the spread of flat rate, the traffic volume in the wireless communication continues to increase. In order to handle such an increase in the traffic volume, it is necessary to expand the frequency band used in the wireless communication system. However, frequency bands such as the UHF band, which are suitable for mobile communication, have already been licensed to various wireless systems. It is thus difficult to license a new frequency band to the existing wireless communication system.
Meanwhile, some frequency bands that have already been allocated to particular systems are not used in some regions or at particular time. There is usage under consideration in which a wireless communication system with high traffic demand temporarily uses such a vacant frequency band (white space) and a shared band not licensed to any wireless system. This usage achieves improvement in the transmission speed of the wireless communication system and efficient use of frequencies.
However, when the frequency band is shared in this way, it is required not to introduce harmful interference to other wireless systems and other base stations in the same system. Especially when the licensed band is used secondarily, reliable protection of the licensed system (primary system) is necessary.
A spectrum control system is presented as a technique to achieve this. FIG. 8 is a conceptual diagram of a wireless system using the spectrum control system. A spectrum control system 10 is connected to a plurality of wireless systems including a wireless communication system and recognizes frequency utilization of base stations 1011 and 1012 in a wireless communication system 1000 and a transmitting station 2011 in other wireless system 2000.
The base stations 1011 and 1012 in the wireless communication system 1000 perform wireless communication with terminals subordinate to the base stations using licensed bands f1 and f2, which are provided to the base stations 1011 and 1012, respectively. Here, suppose that the communication load of the base station 1011 temporarily increases, and a desired communication capacity cannot be satisfied. At this time, the spectrum control system 10 determines a frequency band to be additionally allocated to the base station 1011, transmission power, and an available period, taking into consideration of interference imposed on other wireless systems and other base stations in the same system and regulation regarding frequency use in the corresponding region.
In addition to the above-mentioned licensed band, the base station 1011 secondarily uses a frequency band f3 that is licensed to the wireless system 2000 or uses a shared band f4 that is not licensed to any wireless system, in accordance with allocation by the spectrum control system 10. Then, the communication capacity can be increased.
As a control method of such a spectrum control system, there is a method disclosed in non patent literature 1. FIG. 9 is a system configuration diagram of a wireless communication system disclosed in non patent literature 1.
A network monitoring unit 900 monitors service quality of a wireless communication system. A necessary band evaluating unit 910 evaluates current service quality acquired by the network monitoring unit 900 against a required value so as to evaluate how many additional bands are needed. An available band database (DB) 90 stores a list of available frequency bands according to the position of a transmitting station. An additional band negotiating unit 920 sends parameters including position information of the transmitting station to the available band DB 90 so as to acquire frequency bands available to the transmitting station. The additional band negotiating unit 920 determines the additional band to be used by a base station 1009 based on the available frequency bands and notifies a network setting unit 930 of information of the determined additional band. The network setting unit 930 allocates the additional band to the base station 1009 when the notified additional band is sufficient to satisfy a required value of the service level in the wireless communication system based on the information of the additional band notified from the additional band negotiating unit 920. When the additional band is not sufficient to satisfy the required value of the service level, the network setting unit 930 requests the necessary band evaluating unit 910 to further allocate the additional band.